Intercomparison of210Pb measurements at GEOSECS station 500 in the northeast Pacific

During reoccupation of the GEOSECS-I test station in May, 1979, more than eighty 30-liter Niskin samples were collected in profile, many as replicates, for²¹⁰Pb intercomparison measurements by the WHOI, SIO and Yale groups. In addition to the inter-laboratory comparisons, the SIO group also carried out extensive experiments to test the effect of sample scavenging method. Pb equilibration time (storage effect), and filtration process on the measured²¹⁰Pb results.The intercomparison measurements indicate that there is a general agreement between the various sets of data. The sample set which allows a direct comparison at the same depth was available in most cases only between two of the three groups. The direct paired comparison shows that (1) the WHOI data are systematically 3% lower than the SIO data; (2) there are no systematic differences observed between the SIO and Yale data although the scatter is rather large; (3) the Yale data are systematically higher than the WHOI data by about 8%.The SIO experiments show that (1) the two scavenging methods employed (Fe(OH)₃ and Co-APDC co-precipitation) yield identical²¹⁰Pb results; (2) variation of Pb carrier equilibration time or of storage time has no discernible effect; (3) the filtration apparatus and procedure employed at this station do not result in²¹⁰Pb loss or contamination.The²¹⁰Pb profile structure and absolute concentration measured earlier at the same location (GOGO-II test station and GEOSECS station 347) agree with those of station 500 within 10%. The present profile shows a minimum²¹⁰Pb concentration around 500 m depth, marking the penetration depth of the flux of excess²¹⁰Pb from the atmosphere. There is a mild mid-depth maximum around 2500–3000 m. The²¹⁰Pb/²²⁶Ra activity ratio decreases monotonically from about 1 at the²¹⁰Pb minimum to about 0.5 near the bottom. The particulate²¹⁰Pb profile shows a systematic increase from the subsurface water to the bottom water by a factor of 5. This feature has been observed in many GEOSECS particulate²¹⁰Pb profiles.     

Lithological and Structural Controls on Regional 3-D Fluid Flow Patterns during Greenschist Facies Metamorphism of the Dalradian of the SW Scottish Highlands

Greenschist facies metabasite sills enclosed within phyllitesand psammites of the Dalradian Supergroup of the SW ScottishHighlands have been used as quantitative sensors of fluid flow,from which ‘fossil’ fluid flow-paths have been mapped.Infiltration of H₂O–CO₂ fluid caused carbonation of themetabasite assemblage. Consequently, metabasite sills have developeda characteristic asymmetric zonation of reacted (carbonate-bearing)margins and unreacted (carbonate-absent) interiors. Reactionfront advection theory has been used to constrain the time-integratedfluid flux and flow direction in one dimension, for each sill,from the widths of the reacted margins. Three-dimensional fluxesand flow directions have been constrained from one-dimensionalfluxes by geometrical computation, and regional fluid flow patternshave been deduced. On a regional scale, fluid flow was channelled through phyllitesand focused towards the axial zone of major antiformal foldstructures. Fluid flow was channelled through the 6 km thickArdrishaig Phyllites, within which fluid fluxes were found toincrease exponentially with proximity to the axial surface ofthe Ardrishaig Anticline. Fluid flow through the psammites waslimited to narrow zones of intense deformation associated withmetabasic or phyllitic intercalations. Although time-integratedfluid fluxes were locally high (4 10² m³/m²), average fluxes(100 m¹/m²) are compatible with availability of fluid from underlyingdevolatilizing rocks. Complete isotopic homogenization of phyllites,psammites and metabasites within the axial region of the ArdrishaigAnticline is predicted by these high measured fluxes. KEY WORDS: 3-D flow; Dalradian; SW Scotland; greenschist facies; metabasites ^*Corresponding author. Telephone: 0131-650-5885 Fax: 0131-668-3184 E-mail: askelton{at}glg.ed.ac.uk     

Increasing prevalence of extreme summer temperatures in the U.S.

Human-caused climate change can affect weather and climate extremes, as well as mean climate properties. Analysis of observations and climate model results shows that previously rare (5th percentile) summertime average temperatures are presently occurring with greatly increased frequency in some regions of the 48 contiguous United States. Broad agreement between observations and a mean of results based upon 16 global climate models suggests that this result is more consistent with the consequences of increasing greenhouse gas concentrations than with the effects of natural climate variability. This conclusion is further supported by a statistical analysis based on resampling of observations and model output. The same climate models project that the prevalence of previously extreme summer temperatures will continue to increase, occurring in well over 50% of summers by mid-century.     

云南天文台三孔较差视宁度监视仪的建立

较详细地讲述了云南天文台三孔较差视宁度监视仪的情况,然而,与一般天文理论和天文技术的专题研究不一样,天文仪器的研制有如说是研究,还不如说是归纳;它不是分析一个具体的尚未解决的难题,而是把许多已知的理论和技术综合起来,构成一台具体的仪器。所以,本文把许多至少是表面上互不相关的理论和技术问题归纳到一篇论文中。仪器是有许多模块组成的,为了看起来逻辑性较强,我们将仪器分模块叙述,全文遵循如下顺序：１在第一篇中,回顾世界各天文台视宁度测量设备的发展史和云南天文台的宁静度测量发展史;２在第二篇中,介绍：１）云南天文台三孔较差视宁度研制任务的来源,仪器的整体状况;２）介绍云南天文台三孔较差视宁度仪的硬件系统;３）介绍云南天文台三孔较差视宁度仪的软件系统;若大模块中有多个小模块,在每一个大模块中,又遵循下述顺序：１）本模块的总体功能;２）构成该模块的基本技术;３）这些基本技术如何构成整体和完成预定功能。３在第三篇中,介绍我们所作的与视宁度测量有关的一些实验和实验结果。     

Al hematites prepared by homogeneous precipitation of oxinates: material characterization and determination of the Morin transition

A novel method for synthesis of aluminium hematites, based upon the homogeneous precipitation of Fe and Al oxinates in various proportions, is presented. The precursor precipitates are heated in air at 700?°C. X-ray diffraction, thermal analyses, BET, FTIR, optical reflection analysis, TEM and Mössbauer spectroscopy at room temperature and 80?K of the resulting products indicate that single-phase hematites are formed with structural Al substitution of up to 10 at%. Interestingly, the particle size (>100?nm) is not substantially reduced by the Al content. Although it remains difficult to obtain a homogeneously distributed Al substitution in the final hematite, this processing line offers a unique opportunity to separate the effects of grain size and Al substitution on the Morin transition temperature (T _M) of Al hematite. From the comparison between the present hematites and a series of Al-substituted hematites with lepidocrocite as precursor, it could be shown that the effect on T _M, associated with a change of a factor 10 in grain size, is about 1/3 of the effect caused by a change of 10 in the degree of substitution. Finally, it is suggested that proper thermal treatments under different conditions of the same precursors are likely to produce spinel phases.     

A search for soft X-ray emission from stellar sources

With the soft X-ray detector (0.2–0.284 keV) aboard the Astronomical Netherlands Satellite (ANS) we have searched for X-ray emission from hot star coronae and peculiar stars. On Sirius ( CMa) and Capella ( Aur) X-ray emission has been measured at 6 and 5 level, respectively, above background. In all other cases the search revealed no evidence for soft X-ray emission. Upper limits to the luminosities of about 25 star coronae (main-sequence stars, (sub)giants, and supergiants) and of 4 peculiar stars ( Sco, Lyr, P Cyg, and Car) have been obtained.Paper presented at the COSPAR/IAU Symposium on Fast Transients in X-and Gamma-Rays, held at Varna, Bulgaria, 29–31 May, 1975.     

Dating of Quaternary Sediments from Western Borneo, Using Optically Stimulated Luminescence

Optically Stimulated Luminescence (OSL) dates from five sites in western Kalimantan are compared with ¹⁴C and thermo-luminescence dates from other sediments in the region. There is now strong evidence that the Old Alluvium of Peninsular Malaysia is of late Pleistocene age and that it can be correlated with the White Sand Complexes of western Borneo. This contrasts with the late Pliocene to mid Pleistocene ages for Old Alluvium, based primarily on stratigraphic deductions, put forward by geoscientists examining the regional tin deposits. This study shows that the upper parts, at least, of the western Borneo White Sand Complexes were deposited mid-way through the last glaciation (76 ka), with extensive terminal Pleistocene re-deposition (11.2-9.8 ka) and at least two gully erosion events during the Holocene (5.8-3.8 ka and 0.48 ka).     

Eruption episodes and magma recharge events in andesitic systems: Mt Taranaki,New Zealand

Eruption episodes, where a series of eruption events are generically related, can include the eruption of a wide spectrum of volcanic activity over decadal periods. This paper concentrates on the opening phases of an eruption episode which occurred approximately 1800 yrs BP from Mt Taranaki, New Zealand. These events spanned the eruption of differing bulk compositions and styles from two distinct vent locations; an andesitic sub-plinian eruption from the summit vent and a scoria cone-building eruption of basaltic magma from a satellite vent. Compositional profiles and zoning textures of plagioclase, amphibole and clinopyroxene phenocrysts from the opening andesitic event show evidence of magma mixing and subsequent crystallisation just prior to the initiation of the eruption episode. Titanomagnetite grain morphology and Ti variation suggest that the magma mixing event occurred within a few days to weeks before the eruption acting as a trigger for it. We present a magmatic model which is constrained by the petrological observations and eruptions of the episode. In this model magma differentiation at depth causes its rise and recharging of a mid-crustal magma storage area at 5–7 km. Although the recharging magma differed slightly in oxygen fugacity and temperature, it was compositionally and physically similar enough to the residing andesitic magma to allow efficient mixing. The petrological characteristics described here can be readily observed and enable identification of mixing events in other recent eruption episodes.     

Thermal and topographic tests of Europa chaos formation models from Galileo E15 observations

Stereo topography of an area near Tyre impact crater, Europa, reveals chaos regions characterised by marginal cliffs and domical topography, rising to 100-200 m above the background plains. The regions contain blocks which have both rotated and tilted. We tested two models of chaos formation: a hybrid diapir model, in which chaos topography is caused by thermal or compositional buoyancy, and block motion occurs due to the presence of near-surface (1-3 km) melt; and a melt-through model, in which chaos regions are caused by melting and refreezing of the ice shell. None of the hybrid diapir models tested generate any melt within 1-3 km of the surface, owing to the low surface temperature. A model of ocean refreezing following melt-through gives effective elastic thicknesses and ice shell thicknesses of 0.1-0.3 and 0.5-2 km, respectively. However, for such low shell thicknesses the refreezing model requires implausibly large lateral density contrasts (50-100 kg m⁻³) to explain the elevation of the centres of the chaos regions. Although a global equilibrium ice shell thickness of ≈2 km is possible if Europa's mantle resembles that of Io, it is unclear whether local melt-through events are energetically possible. Thus, neither of the models tested here gives a completely satisfactory explanation for the formation of chaos regions. We suggest that surface extrusion of warm ice may be an important component of chaos terrain formation, and demonstrate that such extrusion is possible for likely ice parameters.